Ultrasound transducers are widely used in many different fields including ultrasound imaging. In many modern medical imaging applications, ultrasound transducers are made of piezoelectric materials. One commonly used piezoelectric material is lead zirconate titanate (PZT). However, the impedance of PZT is usually higher than 30 MRayls while the impedance of human tissues is around 1.5 MRayls. In order to reduce this huge impedance mismatch, one or more matching layers are often placed between the PZT transducer and the tissue being imaged. Since the matching layers are typically selected based on the one-quarter-wavelength principle, the bandwidth of PZT transducers having matching layers may be limited to 80% or less bandwidth.
Traditionally, ultrasound transducers are arranged in one-dimensional (1D) arrays. For example, a 1D array transducer may include multiple elements arranged in only one dimension, e.g., the lateral dimension. In another dimension, e.g., the elevation dimension, however, the aperture of a 1D transducer is fixed. Since the aperture size is increased with penetration depth to maintain uniform elevation slice thickness, the imaging performance of a 1D transducer is compromised due to its fixed elevation aperture. One solution to this problem is to use a 1.5D transducer array. For example, a 1.5D transducer array may include at least two sub-elements in the elevation dimension. The spacing between the two adjacent sub-elements may be much larger than the wavelength. Further, the number of sub-elements may increase with penetration depth for optimal imaging performance from near field to far field. The number of elements and sub-elements of 1.5D arrays is usually significantly larger than the number of channels of the respective imaging systems. Therefore, high voltage analog switches may be used for selecting desired sub-apertures of 1.5D arrays.